Circuit breaker



June 12, y1945*. A. A. BoLsTERLl 2,378,124

CIRCUIT BREAKE Filed March 26, 1942 5 Sheets-Sheet l A4, ATTORNEY Z June 12, 1945. A. A. BoLsTERLl I CIRCUIII1 BREAKER Filed March 26, 1942 5 Sheets-Sheet 2v lll-Ill June. 12, 1945.. A. A. BOLSTERLI CIRCUIT BREAKER Filed March 26,' 1942 I5 Sheets-Sheet 3 K. Q?aw Kw ATTORNEY Patented June 12, 1945 mesne assignments, to Realty and Industrial Corporation, Convent, N. J., a corporation of New Jersey Application March 26, 1942, Serial No`..43`6,264

(Cl. 20o- 147) Claims.

This invention relates to the air type of circuit breaker whereinan arc chute is provided above the circuit'. breaking contacts for dissipating and extinguishing the arc. A

The main object of the invention is to provide a relationship of contacts and auxiliary parts which will Vresult in an effective extinguishment of the arc without objectionable deterioration of Another object is to provide an.

the contacts. improved form of apparatus wherein 'the maintenance of the full voltage on the parts -within the arc chute, or at the entrance thereof, is avoided. 'I'his invention insures that after the arc is extinguished, the potential is removed from one oi the portions between where the arcis formed; and this overcomes any tendency of leakage currents or flash-overs which might otherwise occur upon deterioration of the insulating qualities of the arc chute lresulting from long continued use. Another object is to provide an air type of circuit breaker adapted for carrying currents of comparatively high amperage and for of the lingers between the copper strap 4 and the contact plate 1. An auxiliary copper strap 9 is bolted at one'end to the lower portion of the plate l and at its other end to the conductor 4 for forming an additional electrical connection be-- tween the plate 4 and the plate 1 and for avoiding any arcing between the lingers 8 and the plate l.

The upper conducting lead or terminal A3a is connected at its front end toa U-shaped conducting strap 4a' having downwardly extending sides. A U-shaped bracket 5a is clamped between the plate 4a and the bushing 2 and extends forwardly for supporting between its sides a rod lila for freely pivotally supporting a series pf contact plates I0 similar to the contact fingers use with circuits having comparatively high voltages. Other objects and advantages will be understoodfrom the following description and accompanying drawings which illustrate preferred embodiments of the invention.

Fig. 1 is a side elevation partly in section showing one form of circuit breakerA embodying the invention; Fig. 2 is a front' View thereof partly in section with some parts removed; AFig. 3 is aside elevation partly in section showing another form of circuit breaker; and Fig. 4 is a front view there-` of partly in section.

Referring to Figs. 1 and 2, the breaker is supported upon a main supporting panel I which may be formed of a steel plate. This supports a pair of insulating bushings 2 through which extend the conducting leads or terminals of the ybreaker in the form of heavy copper rods` 3 and 3a. At the front end of the rod 3 is bolted a heavy copper strap 4 of U form; and between the inner portion of this strap and the end of the bushing 2 is clamped a metal plate 5 of U f form with outwardly extending sides. The front portions of these sides form a bearing for the contact armwhich is shown as a. pair of upwardly extending plates 6. On the inner sides f these plates is secured a copper contact platel of U and are freely pivoted at their lower ends on a.

crossbar 8a extending between the sides of the supporting plate 5. Between each pair of con- 8. Between each pair of plates l0 is a-rod lbxed at its front end to the conducting plate 4a and supportingY at its rear end spring pressure means luc for forcing the plates Il) into engagement with the fixed conducting plate 4 andthe conducting plate I when the breaker is in closed position. A

A secondary contact il carried by the arms 6 is electrically connected bycopperstraps I2 to the contact plate l. The contact I I engages another secondary contact I3 provided at-its back with a metal arcing horn i3d which extends upwardly and connects electrically at its lower end vwith a pivotally mounted conducting piece i3d and is separated a large portion of its length from the horn i3d by insulation |3b. The upper end of the `conducting block I3c is pivoted within a hook-shaped conducting element I3e which in turn is fixed to the conductor 4a. A spring I3f passes through the front leg of the conductor 4a and the lower portion of the conducting bearing I3e and is supported at its inner end to engage and exert an outward pressure on the pivoted block I3c for securing good contact engagement between 'the secondary contacts I I and I3 when the breaker is closed. y

Between the upper ends of the arms S is xed a conducting casting I l having a curved inner arcing contact I4a and an upper contact surface I4b. The'conducting casting I4 is connected by the conducting plate I4c to the conducting straps I2 'and thence to the contact plate l.. The contact I4a in the closed position of the breaker engages an arcingcontact I5 which is xed tol a conductor I5a which has an arcing horn at its upper end `and extends downwardly .back of the contact i5 and then upwardly where its upper end is ingood electrical connection with and xed to a cylindrical conducting block I5b. The

v two portions of the conductor |5a areV separated tactors 8 is a rod 8b which is fixed at its front p by an insulating strip Iic and clamped together by a `bolt I5i which is insulated from the inner portion of the conductor.

The cylindrical conducting block |511 is seated 4 in a bearing formed in a casting I 6 with which it makes good electrical contact.A The casting has a downwardly extending front portion for limiting the outward movement of the conductor Ia by engagement with the surface IGa of the casting. This casting extends rearwardly and is fixed to the front side of the rear insulating plate I1 of the arc chute which in turn is supported by a post insulator I8 fixed to the panel plate I. A metal element forming an arcing horn I6b extends from the casting I8 and upwardly against the inside of the insulating plate Il. A blow-out coil I9 is supported within the casting I6 and has a slotted iron core 19a to the ends of which are secured iron or steel plates I9b for creating a magnetic field for forcing the are upwardly through the chute. The blow-out coil is indicated as having a flat copper strap wound edgewise, one terminal I9c of which is secured to the casting I8, the other terminal extending downwardly and secured at its lower end to the side of a U-shaped conductor 20 which in turn is bolted to the top of the conductor 4a. A spring 2l is secured at its inner end to the casting I6 and at its outer end to the contact assembly I5 and I5a for the purpose of forcing it outwardly towards the contact I4a.

The arc chute is closed at the front by an insulating plate 2l and on the sides by insulating plates 22 which may be of nbre or other suitable material and may be lined within by asbestos sheets. The chute above the arcing contacts is provided with cross partitions or bars for breaking up andA cooling the arc but as these form no part of the present invention, they are not indicated.

On the inside of the front plate of the chute is mounted another element forming an arcing horn 23 extending upwardly from a casting having an arcing horn element or surface 24. A second casting 25 below the other casting and spaced therefrom is bolted at one end to the front plate 2I of the chute, the upper casting being supported from the lower casting by a strip 26 of insulating material. A blow-out coil 21 is positioned between the two castings and is provided with a slotted iron core 21a. Iron or steel plates 2lb are mounted on the opposite ends of this core in the usual manner for creating a magnetic eld for forcing the arc upwardly. One end of the edge-wound winding of the blowout coil is connected to the upper casting having the horn element 24 and the other end is connected to the lower casting 25. A movable contact block 28 is pivotally mounted at one end within the curved end portion of the casting 25 and is normally pressed outward by a spring 28a which is positioned between the contact block 28 and casting 25.

I'he contact arms 8 may be actuated on their pivot to closed position in any suitable manner but in the present case provision is made for delaying the opening action in the latter part of the stroke. The arms are shown with forward extensions 6a and between them is pivotally connected a rod 28 of insulating material. This is pivotally connected between a pair of arms 38 xed to a square shaft 3l journaled in xed bearings at its ends. A pair of links having oppositely extending portions 32 and 32a is likewise xed to the shaft 3I. The portion 32a is pivotally connected to links 33 which are in'turn pivotally connected to a pivoted bar 34. The latter may be actuated by any means but is shown as operated by a solenoid indicated at 35.

'I'he portion 32 of the links xed to the shaft 3I is controlled by retarding means in the form of a dashpot. This is shown as having a cylinder 36 pivoted on a xed pivot. Slidable within this cylinder is another cylinder 36a, the upper end of which is pivotally connected to the portion 32. A stem 36h is iixed at its lower end to the bottom of the cylinder 36 and carries a cone-shaped head 36C opposite the end of the cylinder 38a but at a short distance therefrom when the breaker is closed. The cylinder 36 is about half lled with oil or other suitable liquid and an air vent is provided in the upper end of the cylinder 36a.

The breaker is brought to the closed position shown by a downward pull on the links 33 as by energizing the solenoid 35 or otherwise. This turns the shaft 3I clockwise and closes the breaker by the toggle action of the links 30 and rod 29. When the closing action starts, the cylinder' 36a of the dashpot is well within the cylinder 38 and retards the closing movement in the first portion of the stroke; but before any of the contacts are closed, the head 38e passes from within the cylinder 36a which gives free movement to the cylinder 36a and permits a quick closing of the breaker in the latter part of its stroke. When the breaker is opened by the deenergization of the closing coil, or the release of the latching means or otherwise, the opening movement is rapid in the first part of the stroke but retarded in the latter part because the head 36e then enters the cylinder 36a.

In the closed position of the breaker, the main circuit is closed from the lower conductor 3 through the conductor 4 and contact ngers 8 to the plate 'I and thence through the contact fingers I0 through the conductor 4a to the conducting lead 3a. When the breaker is opened, the initial break in the circuit occurs between the plate I and the contact iingers I8. This transfers the path of the current from the plate l through the secondary contacts I I and I3 and by the conducting block I3c to the conductor 4a and to the lead 3a, Upon further opening movement of the contact arm the next break in the circuit occurs between the secondary contacts and thereby shifts the path of the current from the plate 1 to the arcing contacts I4a and I5 and thence to the casting I6 through the blow-out coil I9 to the conductors 28 and 4a to the lead 3a. rI'his places the blow-out coil in the circuit which is thereby energized for driving upwardly the arc between the contacts I4a and I5 when the latter are nally separated upon further opening movement of the breaker. During the opening movement the spring 2I causes the contact I5 to maintain engagement with the contact I4a until the contact I4b is well under the arcing horn 24. At.

the time these arcing contacts separate, the contact surface I4b is about to engage the yieldable contact 28; and as the arc passes upwardly along the horn of the conductor I5a to the casting I6, the arc is transferred to the horn 24 as the contact Hb passes under the horn 24 and engages the contact 28. This then places the blow-out coil 21 in circuit by a path from the contact arm of the breaker to the contact 28 and thence through the blow-out coil 21 to the horn 24 across the arc gap to the casting I6.v The two blow-out coils then cooperate to drive the arc upwardly, the

length of the arc being increased as it is forced upwardly between the horns 23 and I6b and then into the arc chute where it is extinguished. In

the meantime the contact I4bmaintains engagement with the contact 28 during the continuing open movement of the breaker; and before the contact-'Mb leaves the contact 28, the arc has been extinguished. Consequently upon the continued opening movementl of the breaker arm and the separation of the contact |4b from the contact 28, there is no current passing and no arc is formed when these contacts separate. The fully open position of the contact arm is indicated by dotted lines in Fig. 1 which introduces a large air gap between the contact Ma and the, tip ofl the contact 28 by movement of the contact arm away from and beyond the contact 28 and its connected parts. In this manner the potential of the circuit is removed from the horns 24 and 23 and their adjoining parts which effectively prevents the possibility of leakage currents or nashovers from them to the casting I6 and the horn i6b which otherwise might occur, particularly when the insulation quality of the arc chute has deteriorated after long continued use.

In order to insure that the arc will be extinguished before the contact |4b leaves the contact 58 carried by a pair of straps 58a which are piv- 28, there should be a delayed action of the circuit t breaker arm' inthe lattenpart of the opening stroke. Any suitable means may be provided for this purpose and in Fig. 1 this is accomplished by the dashpot action of the parts 36, 36a, 36h and 36e. At the time the contact I4b engages the i contact 28, the cylinder 36a has closely approached the head or piston 36c of the dashpot and asvthe movement continues, the separation of the contact |4b from the contact 28 is'retarded by'the dashpot action. This insures the extinguishment of the arc in the arc chute where the parts are specially provided for its'rapid and eillcient interruption, instead of permitting the arc to be formedbetween the contacts |4a and 28 when they are iinally separated.

Figs. 3 and 4 show another embodiment of the invention. Here the steel panel plate I supports the insulators 2 through which pass the conducting terminals 3 and 3a having contact blocks `4|! y and 40a at their front ends. The block'48 is proi l5 to |5dfof Fig. 1; The arcing contact 45 is supported by and in electrical connection with an arcing horn element 46. vIt is also electrically connected with a terminal of a blow-out coil 41, the other terminal of which is electrically connected to ythe block 40a and terminal 3a of the breaker.. The horn element 46 is electrically connected with oneterminal of another larger upper blow-out coil 48,`the other terminal of which is connected to the blow-out coil 41 and thence to the block 40a and terminal 3a of'fthe breaker. Li'The blow-out coil 48 is provided with iron orsteel side plates 48 which extend outwardly along the inner sides of the arc chute 60y and the blow-out coil. 41 is similarly provided with magnetic plates extending outwardly on opposite sides ofthe contacts 44 and 45. These blow-out. coils and the by post insulators 5l from the panel plate l. Another arcing horn element 52 is mounted on the inside of the iront plate of the chute and exoted at .its lower end ,by a support on the front of the arc chuteextends upwardly and engages the fixed contact 63. At opposite sides of the blade 64 and mounted on the pivot of the blade is a pair of arms 55 from the front ends of which extend a pair of springs 66 which are pivotally connected to the blade 54 at an intermediate portion thereof. The lower ends of the arms 55 are connected to a pair of links 51 which extend rearwardly and converge to form a tube having a pin and slot connection with anothertelescoping tube otally connected to the arms 42 of the breaker. A pair of arms 58 are supported from the switch frame and arc chute and extend forwardly and are joined together at their front portions to form a stop ,for the switch blade 54 when it is in its open position as indicated by the dotted lines.

The pivoted arms 56 are provided with extensions 55a which are connected by a pin forming a pivot for a link 60 which extends upwardly and y engages a pin 6 la by a slot connection at its upper breaker is opened by release of the holdingA end. This pin is carried between a pair of lever arms 6| which are pivotally mounted atlb on a pin supported from the arc chute. Thearms 6| carry a roller Sic between their lower ,ends which is positioned opposite the inner edge of the blade 64 at an intermediate portion thereof,A The blade y 64 is electrically connected by conducting straps 62 with the block 40.

The breaker is shown as actuated to its closed position by a solenoid 35 and connecting parts to the circuit breaker arm/12 similar to those described with reference to Fig. 1 and designated by corresponding reference characters. Likewise the same form of means for delaying the opening action of the breaker in the latter part of its stroke is shown in the form of a retarding dashpot like shown in Fig. 1.

The breaker is shown in its closed position in Fig. 3, the conducting plate 42a and the contacts 43 and 43a serving vas the main path forv the current between the terminals 3 and 3a. When the means, the rst separation of the contacts takes place between the contactgplate 42a and contacts 43a, thelpath vof the current them being transferred through the arcing contacts 44 and 45 and through the blow-out coil 41 to the terminalsq, As the opening movement continues, the spring pressed contact 45 is forced forwardly maintaining an engagement with the-y contact 44 until the contact 45 engages itsstop. An arc is then drawn between these contacts as they separate and the blow-out coil 41 serves to force\\the`arc upwardly.

` The continued opening moveme t causes the conhorn 46 andcontact assembly 45 are supported l.

tact'44 to pass close to the hov 52 which results in the arc being transferred to andv between the horns 52 and 4K6. The path of the current is then from lthe lead or terminal. 3 to the block 48 and f thence by the straps szithroughtiie switch blade 54 to the horn 52 and then by the arc to the horn 48 through the blow-out coil 48 and coil 41 to the block 40a and tl'ien the terminal lead 3a. This f brings the blow-out coil 48 into action which forces the arc upwardly between the hornsv 52 and v46 into the arc chute where it is extinguished. After the arc has been extinguished in this manner, the continued opening movement of the con tends towards the horn 46 and also has a portion 75 tact arms 42 to 'their iinal position as indicated by the dotted lines, causes the connection between the arms 42 and the levers 55 to turn the latter in a clockwise direction. This throws the lower ends of the compression springs 56 inwardly past their dead center position and thereby throws the switch blade 54 outwardly to its dotted positionV as shown in Fig. 3. In case the blade 54 should stick and the springs 56 fail t0 throw it to the open position, the link 60 and its connecting parts will insure the opening of the switch because it is moved downwardly by the lever 55 and after a certain amount of movement will engage the pin Glo: and force the roller Sic against the inner edge of the blade 54 and force it outwardly from the xed contact 53. The springs 56 will then hold this blade in its open position. The opening of this switch removes the potential of the circuit from the horn 52 and thereby prevents the possibility of leakage currents or flash-overs to the horn 46 when the circuit breaker is open.

Although the are may be extinguished in the chute before the switch blade 54 is moved to its open position by the lost motion of the parts and design of the switch, means for delaying the movement of the contact arms in the latter portion of the stroke is provided for insuringlsuch sequential action. This is provided in Fig. 3 by the dashpot form of control like that described with reference to Fig. l and any possibility of arcing between the switch blade 54 and the xed contact 53 is thereby avoided when this switch is opened.

When the circuit breaker is actuated to its closed position, the mechanical connections between the contact arms of the breaker and the switch blade 54 will cause the lower ends of the springs 56 to be swung from the inner side to the outer side of the centerline from the upper ends of the springs to the pivot of the arms 55 and thereby snap the switch blade 54 to its closed position. During this movement the link 60 will be moved upwardly and remove the roller 6 lc from the path of the switch blade in its movement to closed position. This brings the parts to the position shown in full lines in Fig. 3 in readiness for functioning in the manner already described when the circuit breaker is opened again.

Any desired number of single pole circuitbreakers of the character described may be mounted side by side and simultaneously controlled in their closing and opening movements For example, Fig. 4 shows a supporting frame 61 with spaces provided at the sides of the single pole breaker already described for the reception` of two additional units, such a-s for the control of a three-phase supply line. The additional poles would be simultaneously controlled by movement o'f the shaft 3i with toggle connec tions therefrom to the respective poles.

Although particular embodiments of this 'invention have been described, various modifications may be made and adaptations for particular requirements without departing from the electrically connecting the contact arm to said second element during the opening movement of the contact arm for thereby transferring the arc to said elements during the opening movement and for electrically disconnecting said Contact arm from said second element in the vlatter part of the opening movement of the contact arm by movement of the contact arm beyond and away from said second element.

2. A circuit breaker comprising a movable contact arm, a contact engaged thereby in the closed position of the arm, an arc chute, a horn element for carrying the arc positioned above said engaged contact at one wall of the arc chute and electrically connected with said engaged contact, a second horn element for carrying the arc elec trically disconnected from said rst named element and positioned at the opposite wallof the arc chute, means for electrically connecting the contact arm to said second element during the opening movement of the contact arm for thereby transferring the arc to said elements during the opening movement and for electrically disconnecting said contact arm from said second ele,- ment in the' latter part of the opening movement of the contact arm, and means for retarding the movement of the contact arm during the latter part of its opening movement for providing a time interval for extinguishing the arc before electrically disconnecting the contact arm from Ysaid second element.

, 3. A circuit breaker comprising a movable contact arm, a contact engaged thereby in the closed position of the arm, an arc chute, a horn element for carrying the arc positioned above said engaged contact at one wall of the arc chute and electrically connected with said engaged contact, a second horn element for. carrying the arc electrically disconnected from said rst named element and positioned at the opposite wall of the arc chute, means for electrically connecting the contact arm to said second element during the opening movement of the contact arm for thereby transferring the arc to said elements during the opening movement and for electrically disconnecting said contact arm from said second element in the latter part ofthe opening movement of the contact arm, and a dashpot mechanically related to 'the contact arm for retarding the movement of the Contact arm during the latter part of its opening movement for providing a time interval for extinguishing the arc before electrically disconnecting the contact arm from said second element.

4. A circuit breaker comprising a movable contact arm, a contact engaged thereby in the closed position of the arm, an arc chute, a h orn element for carrying the arc positioned above said engaged contact at one wall of the arc chute and electrically connected with said engaged contact, a second' horn element for carrying the arc electrically disconnected from said ilrst named element and from said contact arm and positioned at the opposite wall of the arc chute, a blow-out Vopening movement' of the contact arm for thereby transferring the arc to said elements during the opening movement and for electrically disconnecting said contact arm from said second element in the latter part of the opening movement of the contact arm by movement of the contact arm beyond and away from said second element.

5. A circuit breaker comprising a movable contact arm, a contact engaged thereby in the closed position of the arm, an arc chute, a horn element for carrying the arc positioned above said engaged contact at one wall of the arc chute and electrically connected with said engaged contact,

a second horn element for carrying the arc electrically disconnected from said first named element and from said contact arm and positioned at the opposite wall of the arc chute. a blow-out magnet electrically connected in circuit between said iirst named element and said engaged contact, a second blow-out magnet connected in circuit from the contact arm during its opening movement to said oppositely positioned element, and means for electrically connecting the contact arm to said second element during the opening movement of the contact arm for thereby transferring the arc to said elements during the opening movement and for electrically disconnecting said contact arm from said second element in the latter part of the opening movement of the contact arm by movement of the contact arm beyond and away from said second element.

6. A circuit breaker having a movable contact arm, a terminal electrically connected with said contact arm, a second terminal electrically connected with the contact arm in the closed position of the arm, an arc chute, a horn element for carrying the arc positioned above said second terminal at one wall of `the arc chute and electrically connected with said second terminal, a second horn element for carrying the arc positioned at the opposite wall oi' the arc chute, the contact arm in its opening movement passing from near said first named element towards said oppositely positioned element for transferring the arc to said elements, an auxiliary switch electrically connected to said oppositely positioned element and to said first named terminal, and means controlled by the contact arm in the latter part of its opening movement for opening said switch for disconnecting said oppositely positioned element from said first named terminal.

7. A circuit breaker having a movable con t arm, a terminal electrically connected with said contact arm, `a second terminal electrically connected with the contact arm in the closed position of the arm, an arc chute, a horn element for carrying the arc positioned above said second terminal at one wall of the arc chute and electrically connected with said second terminal, a second horn element for carrying fthe arc positioned at the opposite wall of the arc chute, the contact arm in its opening movement passing from near said rst named element towards said oppositely positioned element ior transferring the arc to said elements, an auxiliary switch electrically connected to said oppositely positioned element and to said ilrst named terminal, and means controlled by the contact arm in the latter part of it/s opening movement for opening said switch for disconnecting said oppositely positioned element from said first named terminal, said means comprising a spring for opening said switch and supplemental means mechanically connected with the contact arm for forcing said switch open, l ff 8. A circuit breaker having a movable contact ann, a terminal electrically connected 'with said contact arm, a second terminal electrically connected with the contact arm in the closed position of the arm, an arc chute, a horn element for carrying the arc positioned above said second terminal at one wall of the arc chute and electrically connected with said second terminal. 'a second horn element for carrying the arc positioned at the opposite wall of the arc chute, the contact arm in its opening movement passing from near said first named element towards said oppositely positioned element for 'transferring the arc to said elements, an auxiliary switch electrically connected to said oppositely positioned element and to said first named terminal, means controlled by the contact arm in the latter part of its opening movement for opening said switch for disconnecting said oppositely positioned element from said first named terminal, and means for retarding the movement of the contact arm during the latter part of its opening movement for providing a time interval for extinguishing the arc before opening said switch.

9. A circuit breaker having a movable contact arm, a terminal electrically connected with said contact arm, a second terminal electrically connected with the contact arm in the closed position of the arm, an arc chute, a horn element ior carrying the arc positioned above said second terminal at one wall of the arc chute and electrically connected with said second terminal, a second horn element for carrying the arc positioned at the opposite wall of the arc chute, the contact arm in its opening movement passing from near said first named element towards said oppositely positioned element for transferring the arc to said elements, an auxiliary switch electrically connected to said oppositely positioned element and to said first named terminal, means controlled by the contact arm in the latter part of its opening movement for opening said switch for disconnecting said oppositely positioned element from said first named terminal, and a dashpot mechanically related to the contact arm for retarding the movement of the contact arm during the latter part of its opening movement for providing a time interval ior extinguishing the arc before the opening of saidswitch.

10. A. circuit breaker comprising a movable contact arm, said arm having a main contact and an arcing contact, a terminal electrically connected with said arm, a second terminal having a main contact and an arcing Contact respectively engaged by said main contact and arcing Contact of the Contact arm when the breaker is closed, an arc chute, a horn element for carrying the arc positioned above said second terminal of the breaker at one wall of the arc chute, a second horn element for carrying the arc electrically disconnected from said first named element and from said' contact arm and positioned at the opposite wall of the arc chute, the contact arm in its opening movement passing from near said first named element towards the oppositely positioned element for transferring the arc to said elements and for electrically disconnecting said contact arm from said second element in the latter part of the opening movement of said contact arm by movement ol' the contact arm beyond and away from said second element, a blow-out ir net connected in circuit between said second nal and its arcing contact for acting on the aro between said arcing contacts, and a second blow-out magnet connected in circuit between said first named element and said second terminal for acting on the arc between said elements.

ARTHUR A. BOLSTERLI. 

